Abstract
A one-body point absorber (PA) is a type of water wave energy converter (WEC) that generates power from the relative motion of a floating body with respect to a fixed reference frame. The size constraints of the one-body PA WEC limit its energy capture around the low frequency range of ocean waves. In this paper, inspired by the concept of point defects in phononic crystals for acoustic and elastic energy harvesting, we seek to enhance the energy harvesting performance of a PA WEC by placing it at the defect of an array of heaving cylinders in water. Moreover, for the first time, we aim to gain a deep understanding on how the creation of these modes can increase the motion of a PA WEC over a broad range of frequencies. First, we calculate the band structure and surface elevation of a 3 by 3 array of both fixed and heaving cylinders to study the modes that arise from the creation of a point defect. Then, with a PA WEC placed at the defect, we conduct an analysis to understand how the design of the surrounding cylinders affects the energy harvesting performance of the PA WEC. For a given sea state, with significant wave height of 1.75 m and period of 8.5 s, we demonstrate that placing the PA WEC at the defect can lead to over 50% more average power than the same device in isolation. More specifically, we achieve this when the surrounding cylinders have a filling fraction of 0.5, and a radius and draft equal to 1.5 and 6 times, respectively, greater than that of the PA WEC. Lastly, an array with three point defects is analyzed for the same sea state. Using a similar design of the surrounding cylinders that was used in the case of a single defect, we show that the average power of three PA WECs placed at the defects leads to an over 50% improvement (when compared to three PA WECs without the surrounding cylinders).